Field of the Invention
This invention relates to semiconductor switches and, more particularly, a photoconductive semiconductor switch (singularly, “PCSS”).
Description of the Related Art
A PCSS may be an electric switch that is based upon the photoconductivity of a material and controlled by light via photon-induced conductivity. Photoconductivity may be considered an optical and electrical phenomenon in which a material becomes more electrically conductive due to an absorption of electromagnetic radiation when irradiated. Where photon energy is sufficient enough to raise electrons above the band gap energy, free electrons are generated and electrical current flows. As number of free electrons and electron holes in the material increases, conductivity increases.
Many materials possessing favorable photoconductive properties are available in the design of PCSSs. Materials such as chromium-doped gallium arsenide (“GaAs”) (collectively, “Cr—GaAs”), low-temperature grown gallium arsenide (“LT-GaAs”), indium phosphide (“InP”), amorphous silicon, and gallium nitride (“GaN”) possess favorable photoconductive properties. Photoconductive materials may serve as semi-insulating (“SI”) substrates in the design of PCSSs.
Known to those skilled in the art, a PCSS may fall into one of two categories: a lateral PCSS and a vertical PCSS. A generic representation of a lateral PCSS comprised of a semi-insulating (“SI”) substrate 102 and metallic electrodes 104 and being irradiated with a laser pulse 106 is shown in FIG. 1A. Similarly, a generic representation of a vertical PCSS comprised of a dielectric 108, an SI substrate 110, and metallic electrodes and being irradiated with a laser pulse 112 is shown in FIG. 1B (only the top metallic electrode 114 is shown, whereas a bottom metallic electrode 116 opposite of the top metallic electrode 114 is hidden from view).
PCSSs may be used in high-power applications requiring, for instance, greater than 10 kilovolts and 10 kiloamps. In addition, PCSSs may be used in directed energy applications such as pulsed power generation, ultra wideband radar, and arbitrary waveform generation, and scaled to provide a near ideal isolated radio frequency (“RF”) switch. PCSS turn-on times of 10 picoseconds may be obtainable and optimized with turn-off times of 10 picoseconds. With transitioning times of nearly zero, PCSSs operating in power devices comprised of binary switches improve class-D amplifiers.
Although PCSSs possess favorable properties in high-power applications, unfavorable properties may exist during the employment of lateral PCSSs comprised of metallic electrodes. Although lateral PCSSs demonstrate high energy conversion efficiency when subjected to front side irradiation (such as shown in FIG. 1A), high electrode resistance is present directly underneath the electrodes. When subjected to back side irradiation, low energy conversion efficiency is demonstrated along with low electrode resistance.